This application claims the priority of 198 42 066.8-21, filed Sep. 15, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a vehicle steering system that can be switched between a normal mode with a steer-by-wire level and an emergency mode with a fall-back level, and to methods for function-checking such a steering system.
In a known type of steering system, a steering handle, e.g. a steering wheel, is actuated by a driver. During normal operation of this steering system, i.e. on its steer-by-wire level, the steering handle is connected to steered vehicle wheels by an electric or electronic control system. Steering commands input into the steering system via the steering handle are converted into steering-angle adjustments of the steered vehicle wheels on the steer-by-wire level by the control system. In the emergency mode of the steering system, i.e. on its fall-back level, the steering handle is positively coupled, mechanically and/or hydraulically, to the steered vehicle wheels. On the fall-back level, a steering actuation of the steering handle is converted directly into a steering actuation of the steered vehicle wheels by the positive coupling.